It is a modification that was written for a much older version of the forums, however I belive I have gotten it to work.

There is now a button in every post next to the Quote, Edit, Delete buttons that says Ignore. Clicking on it will add the person who wrote that post to your Ignore list.

If someone is on your ignore list you will not see their posts. Instead you will get a message saying that this person is on your ignore list with an option to click a link to go ahead and view the post anyways if you desire.

If you change your mind later on you can remove the person from your ignore list.